(USA TODAY) -- As health care workers around the country work frantically to accommodate the millions seeking protection against the H1N1 strain of influenza, they have to contend with a countertrend: significant numbers of Americans who don't plan to vaccinate themselves or their children.

The reasons given are often that they don't think it's necessary, or that they're uncertain about the safety of the vaccine. But one response, given by 69% of parents in a September poll by Consumer Reports, is different. Those parents say they'd rather have their children build "natural immunity" to the flu -- by getting sick.

Robin Li, 35, of San Francisco says she's "a cautious proponent of vaccines in general," especially for illnesses like polio or measles. But she doesn't plan to have her 1-year-old son vaccinated against the flu, seasonal or H1N1.

"I'm just not convinced that never getting sick is a goal for children. I think the body's designed to get sick and build its immune system."

It's not a case of the sniffles

Nationwide, 86 children under 18 have died from H1N1 flu this year, including 11 who died the week ending Oct. 10, the most recent week for which numbers were available. About half of the deaths in children since Sept. 1 were in patients ages 12 to 17, says the Centers for Disease Control and Prevention's Anne Schuchat. " And it's only the beginning of October."

In a normal flu season, which starts in the fall and lasts through spring, the total number of pediatric deaths from flu range from 46 to 88, Schuchat says.

Saiya Darden, 28, of New York City knows the dangers all too well. Her 3-year-old daughter, Chasidy, spent three months in the hospital after contracting H1N1 on June 6.

"I don't even have an enemy that I would wish it upon," Darden says.

It began with a 103-degree fever. "You could feel the heat coming off," Darden says. Chasidy's lungs collapsed, and the doctors had to put her on a ventilator, Darden says.

"She had a tube down her throat," Darden says. "She had IV needles in just about everywhere on her body you could think of, from her feet to her neck."

Chasidy spent three weeks on an artificial heart-lung machine. The blood thinner required "made her start to bleed from her nose, her mouth and her ears."

Today Chasidy is doing "great," Darden says. But the experience has made Darden an advocate of the flu vaccine.

For those who advocate "natural immunity," is there really a difference between the immunity conferred by getting the flu and that provided by vaccination?

They're close, though the nasal-spray type is closer, says Tun-Hou Lee, a professor of virology at the Harvard School of Public Health.

There are three "arms" of the immune response, Lee says. The first are antibodies, which are also known as immunoglobulins. Produced by white blood cells, they identify and attack bacteria and viruses. The second are killer T cells, which can tell when a cell has been infected with a virus and then attack it. The third are mucosal antibodies, which live in the mucous membranes in the nose and mouth and defend against the virus there.

Most vaccine from killed virus

There are two types of vaccine available against both seasonal and H1N1 flu. About 80% is in the form of shots made from killed virus. FluMist nasal spray, which makes up about 20% of the H1N1 vaccine supply, uses live, weakened virus to provoke an immune response.

The live but weakened ("attenuated") virus creates all three immune responses, Lee says. "You can almost treat the FluMist as a natural infection," Lee says. The shots only provoke an antibody response.

One thing that is different is how long the immune response lasts. Flu vaccines confer immunity for one to two years. Actually getting sick with the flu can result in immunity from that particular strain that lasts 20 years or more, CDC tests show. That's why older adults may have a certain degree of protection against H1N1 -- because many of them were exposed to a close cousin of this strain that circulated before 1957.

No life-long immunity

Because flu mutates frequently, unlike diseases such as measles and polio, one shot, or one bout of it, doesn't confer life-long immunity to the disease, only to the particular strain encountered. So neither vaccination nor getting the flu ensure protection against future strains.

Not all in the more alternative wings of the medical profession shun vaccination. Jane Guiltinan, dean of the School of Naturopathic Medicine at Bastyr University in Kenmore, Wash., worries that the public may not realize that mass vaccinations protect those at greatest risk for serious problems from the flu by helping stop the epidemic.

And forget about using foods or herbs to boost your immune system to avoid getting sick in the first place. There's no evidence that works, she says.

What does boost the immune system "is vaccination," she says.

Copyright 2009 USA TODAY, a division of Gannett Co. Inc.